Hearing aid



Aug. 30, 1966 E. EBERHARD ETAL 3,270,146

HEARING AID Filed March 14, 1965 3 Sheets-Sheet l Fig. IA

INVENTOR 5 ATTY'S.

Aug. 30, 966 E. EBERHARD ETAL 3,270,146

HEARING AID Filed March 14, 1963 Q .z Sheets-Sheet 2 "*TO RECEIVER INPUTI I0 TRANSISTOR 26R 26 loo INPUT HOLES FOR TERMINAL CAPACITOR LEADS I08+I.25v INPU TERMIN I06 ll8 TRANSISTOR To RECEIVER Fig. 3

TRANSISTOR I-llB-I I|-I04-| L 28 I l i -IO2* i T'T'l I L I \CAPACITORINVENTORS Everett Eberhqrd Fig. 4 R/chard T. Martin ATTYS.

Aug. 30, 1966 E. EBERHARD ETAL 3,270,146

HEARING AID I Filed March 14, 1963 5 Sheets-Sheet a TO RECEIVER INPUTHOLES FOR CAPACITOR TERMNAL LEADS +I.25v INPUT TERMINAL I TO RECEIVER lgTRANSISTOR 20s 3|8 /TO RECEIVER Fig 7 l NPUT 302 I k 7 mo .5

330 SM 304 313 3'0 HOLES FOR INPUT CAPACITOR TERMINAL LEADS INPUTTERMINAL 318 To RECEIVER 8 INVENTORS Everett Eberhard Richard T MartinBY MKCIM ATTY'S.

United States Patent 3,270,146 HEARING AID Everett Eberhard, Phoenix,Ariz., and Richard T. Martin,

Minneapolis, Minn., assignors to Motorola, Inc., Chicago, 111., acorporation of Illinois Filed Mar. 14, 1963, Ser. No. 265,125 3 Claims.(Cl. 179107) The present invention relates to hearing aids, and itrelates more particularly to an improved miniaturized hearing aid of thetransistor amplifier type.

The improved miniaturized hearing aid unit to be described is completelycontained with-in an extremely small housing. The unit is adapted to beworn directly in the ear, or to be inconspicuously supported behind theear. The unit is preferably symmetrical so as to constitute a dualfitting instrument which can be worn on or in either ear.

Many attempts have been made in recent years to miniaturize hearingaids, so that the entire unit may be supported on the ear. Theseattempts at miniaturization have been made in order to obviate thenecessity for bulky and unsightly equipment about the person of thewearer.

Problems have been encountered, however, in the use of many of the priorart hearing aids of the above mentioned miniature type. This is becausethe space requirements are such that the prior art active circuitscannot be properly encapsulated or otherwise protected. This hasresulted in relatively rapid corrosion in and deterioration of the priorart instruments due to the effects of perspiration, and the like.

The hearing aid of the present invention, as will be described, iscapable of being miniaturized to such an extent that its activecomponents can be encapsulated Without exceeding the weight and spacerequirements of the overall unit. The instrument of the invention,therefore, can be adequately protected against the above mentionedcorrosive and deteriorating effects.

The hearing aid to be described is a fixed-level instrument for mildnerve type hearing losses. The instrument, however, has also proveneffective as a full-time or a part time instrument in the moderate orstrong loss range-s.

An object of the invention is to provide an improved hearing aid of theabove mentioned type which requires a minimum of component parts inorder to achieve its desired purpose, and yet which is capable ofefficient and trouble-free operation.

Another object of the invention is to provide such an improved hearingaid which may be produced on a relatively economical basis and marketedas a relatively inexpensive unit.

Yet another object of the invention is to provide such an improvedhearing aid which may be constructed to occupy materially less volumethan the prior art instruments of the same general type, so as to beappropriate for encapsulation and other like protective measures.

A still further object of the invention is to provide such an improvedhearing aid which is rugged in its construction and which is thereforecapable of withstanding rough usage.

Another object of the invention is to provide such an improved hearingaid which is highly resistant to the adverse effects of moisture andother corrosive agents.

A feature of the invention is the use of thin-filmed conductors andresistors in conjunction with transistors in the amplifier section ofthe instrument. Such a. construction, as will be described, provides anamplifier which occupies about half the volume of the prior artamplifiers of the same general type.

Another feature of the invention is the provision of a hearing aid ofthe miniaturized type for use directly in or on the ear of the wearer,and having an amplifier sec- "ice tion of a size and weight such that itmay be readily encapsulated so as to render the unit highly resistant tomoisture and other corrosive agents.

Yet another feature of the invention is the provision of adjustableshort-circui-ting tabs for use in conjunction with the thin-filmedresistances in the transistorized amplifier section of the hearing aid,so that the resistance of the resistances may be easily controlled totake care of characteristic variations in the different transistors usedin the amplifier section.

Basically, the thin-filmed resistance consists of a conducting film ofcarbon, metal or metal oxides deposited on an insulating substrate. Thevalue of the thin-film resistance is controlled by controlling thethickness and length of the film. The thin-film resistance is usuallycoated with an insulating protective varnish.

In a constructed embodiment of the invention, thin-film resistances havebeen formed by using tin oxide deposited on a ceramic substrate. Theconductors interconnecting such resistances were also formed as athin-film on the substrate, and these conductors were formed ofchromegold, in the constructed embodiment.

The transistorized hearing aid of the present invention utilizes athin-film resistance and conductor construction which, as will bedescribed, makes possible a material size reduction in the activecomponent of the unit. This enables encapsulation techniques to be usedwithout result-ing in an unduly bulky or heavy instrument.

The encapsulation of the active components of the hearing aid of theinvention precludes any possible external contact. Such encapsulationnot only protects the unit from external corrosive effects, but rendersthe assembly extremely rugged from a mechanical standpoint, and enablesit to be subjected to rough usage without the likelihood of damage.

In addition, a flexible circuit construction is provided in the hearingaid unit to be described, this being due to the short-circuiting tabsreferred to above. These tabs provide for adjustable resistors in theamplifier circuit,

and they also form convenient resistor taps. The adjustable resistorfeature of the circuit permits adjustments to be made to accommodatewide characteristic variations which are normally found betweendifferent transistors of the same type. o

Other features and advantages of the invention will become apparent froma consideration of the following description, when the description istaken in conjunction with the accompanying drawings in which:

FIGURE 1A is a side perspective View of, on an enlarged scale, aminiaturized hearing aid unit constructed in accordance with the presentinvention for direct mounting within the ear of the wearer;

FIGURE 1B shows the unit of FIGURE 1A, adapted to be supportedbehind theear of the wearer;

FIGURE 2 is a circuit diagram of a transistorized amplifier appropriatefor use in the unit of the invention;

FIGURE 3 is a plan view of the actual constructional details of theamplifier of FIGURE 2, and illustrating the manner in which thin-filmconductors and thin-film resistors are supported on an insulatingsubstrate;

FIGURE 4 is a side elevational view of the amplifier section of FIGURE3;

FIGURE 5 is a circuit diagram of a transistorized amplifier,constituting a modification of the circuit of FIG- URE 2;

FIGURE 6 is a plan view of the mechanical details of the amplifier ofFIGURE 5;

FIGURE 7 is a circuit diagram of yet another modification of thetransistorized amplifier of FIGURE 2; and

FIGURE 8 is a plan view of the constructional details of the amplifierof FIGURE 7.

The constructional details of a hearing aid unit con- 3 structed toincorporate the concepts of the present invention are shown in FIGURE1A. The unit of FIGURE 1A includes a casing which may have a generallyrectangular configuration.

The casing 10 has a tilted, generally circular portion 12 formed on itsforward wall, and a receiver 14 is mounted on the portion 12. Thereceiver 14 includes the speaker of the unit.

A receiver tip, or earpiece, 16 is detachably mounted on the receiver14. The receiver tip 16 is shaped to extend directly into the ear canalof the wearer to support the entire unit within the ear. The unit issymmetrical so that it can be worn, without any modification, in eitherear.

A fiat, rectangular shaped microphone 18 is supported within the casing10 adjacent the rear wall of the casing, and the rear wall is aperturedadjacent the microphone to permit the sound Waves to impinge on themicrophone. The aperture in the rear wall may be covered by a cloth 20.The microphone 18 is electronically coupled to the receiver 14 by anamplifier section 22. A battery 24 for the unit is mounted in thecircuit portion 12 of the casing.

The unit of FIGURE 1A may be supported inconspicuously behind the ear ofthe wearer by means, for example, of a plastic tube 30, shown in FIGURE1B. The tube 30 extends around the ear, and it includes a coupler 32 atone end which is inserted into the canal. An adapter 34 is mounted onthe other end of the tube. The ear piece 16 in FIGURE 1A is removed, andthe unit of FIGURE 1A may then be clipped onto the adapter 34, as shownin FIGURE 1B.

The amplifier section 22 of the hearing aid unit may be constructed ofthin-film resistances and conductors, as mentioned above. This sectionmay take the form shown in FIGURES 3 and 4, for example, or it may takethe form of FIGURE 6 or 8, or it may take other equivalent forms.

An appropriate transistorized circuit diagram for the amplifier section22 of the hearing aid is shown in FIG- URE 2.

The amplifier of FIGURE 2 includes a pair of input terminals 100. One ofthe input terminals 100 is grounded, and the other is connected to acoupling capacitor 102. The coupling capacitor 102 is connected to thebase of an NPN transistor 104. The emitter of the transistor 104 isgrounded, and its collector is connected to a resistor 106. The resistor106 is connected to a further resistor 108, and to a resistor 110. Theresistor 110 is connected back to the base of the transistor 104.

The resistor 108 may be connected to the positive terminal of aunidirectional potential source (such as the battery 24 in FIGURE 1A)which may, for example, have a potential of 1.25 volts. The capacitor102 may have a capacity of 2 microfarads, the resistor 106 may have aresistance of 1 kilo-ohm, the resistor 108 may have a resistance of 1kilo-ohm, and the resistor 110 may have a resistance of 85 kilo-ohms.

The collector of the transistor 104 is also connected to a capacitor112. The capacitor 112 is connected to resistor 114 and to the base ofan NPN transistor 116. The emitter of the transistor 116 is grounded,and the collector is connected to an output terminal 118. The collectoris also connected to the resistor 114 and to a grounded capacitor 120.

The capacitor 112 may have a capacity, for example, of 2 microfarads.The resistor 114 may have a resistance of 60 kilo-ohms, and thecapacitor 120 may have a capacity of .07 microfarad.

As illustrated in FIGURES 3 and 4, the various components and circuitconnections of the circuit of FIGURE 2 may be mounted on an insulatingsubstrate 122, composed, for example, of ceramic and having arectangular configuration. The various conductors maybe formed on thesubstrate in the thin-film form of chrome-gold conductors, for example;and the various resistors may be formed on the substrate as thin-film,tin-oxide resistances. The thin-film resistances and conductors may beformed on the substrate 122 in the pattern illustrated in FIGURE 3, andthey may be so formed in accordance with appropriate, known thin-filmprocesses.

As shown in FIGURE 4, for example, the transistors 104 and 116 aremounted on one side of the substrate 122, and the capacitors 102 and 112are mounted on the other side. The particular NPN transistor utilized inthe illustrated circuit in a constructed embodiment were of an uncasedsilicon planar type. This type of transistor is especially suited to thepurpose because of the negligible width thereof.

The resistance values of the resistors 110 and 114 may be adjusted to adesired value, dictated by the characteristics of the transistors 104and 116, this being achieved by the use of a multiplicity ofshort-circuiting tabs 126. These tabs are formed over the thin-filmresistors, and the tabs are selectively connected to the adjacentconductor to provide the required resistance value.

The unit of FIGURES 3 and 4 may be encapsulated in a suitableencapsulating compound, as designated by the dotted line 128 in FIGURE4. As mentioned previous ly, the extremely small size of the unitrenders such encapsulation feasible, because of the relatively low massof the encapsulating material required, and because of the relativelysmall overall volume of the encapsulated unit.

As mentioned above, the provision of the shorting tabs 126 provides asolution for the transistor characteristic variation problem. Theresistors 110' and 114 can be adjusted to any desired value, byselectively connecting the short-circuiting tabs to the adjacentconductive film.

The modified circuit of FIGURE 5 is essentially similar to that ofFIGURE 2, except that it provides for higher gain at lower inputimpedance to the transistors 104 and 116. The circuit of FIGURE 5, andthe lay-out of FIG- URE 6, illustrates the versatility of the thin-filmconcept in the combination of the present invention. In the circuit ofFIGURE 5, elements which are equivalent to those in the circuit ofFIGURE 2 have been designated by the same numerals.

In the circuit of FIGURE 5, the input terminals are connected to groundand to the coupling capacitor 102. The coupling capacitor 102 isconnected to the base of the transistor 104. The collector of thetransistor 104 is connected to a resistor 200 which, in turn, isconnected to a resistor 202 and to the resistor 203. The resistor 202 isconnected to the positive terminal of the 1.25 volt direct voltagesource. The resistor 200 may have a re sistance of 550 ohms, theresistor 202 may have a resistance of 1.8 kilo-ohms, and the resistor203 may have a resistance of 96 kilo-ohms, for example.

The collector of the transistor 104 is also connected to the capacitor112 which, in turn, is connected to the base of the transistor 116. Thecollector of the transistor 116 is connected to the output terminal 118and to a resistor 204 and to 120. The resistor 204 is connected to thejunction of a pair of resistors 206 and 208. The resistor 206 isconnected to the positive terminal of the 1.25 volt direct voltagesource, and the resistor. The resistor 204 may have a resistance, forexample, of 12.5 kilo-ohms, and the resistor 206 may have a resistanceof 22.5 kilo-ohms, and the resistor 208 may have a resistance of 124kiloohms.

The various components of the circuit of FIGURE 5 may be mounted on thesubstrate 122 in the manner shown in FIGURE 6. Again, the technique ofthin-film resistance and thin-film conductor deposition is used to formthe amplifier section. Short-circuiting tabs 126 are provided on theresistors 203 and 208, and these tabs may be selectively connected tothe adjacent conductors, to make the necessary adjustments in'theseresistors to compensate for variations in the characteristics of thetransistors 104 and 116.

It Will be appreciated that the circuit lay-out of FIG- URE 6 has atotal of two adjustable resistors, and the equivalent of four fixedresistors. However, the lay-out of FIGURE 6 can be placed in the samespace as the original thin-film lay-out of FIGURE 2, which incorporatesbut two adjustable resistors and two fixed resistors.

As mentioned above, the circuit of FIGURE 7 is generally similar to thatof FIGURE 2. In the embodiment of FIGURES 7 and 8, however, germaniumtransistors 300 and 302 are used preferably, so as to achieve a higherpower level, and to achieve this with a minimum of transistor cost. Inthe embodiment of FIGURES 7 and 8, the substrate 304 is provided withtwo relatively large holes 306 and 308 for receiving the transistors 300and 302. The substrate is formed of suitable insulating material such asceramic.

The circuit of FIGURE 7 includes a pair of input terminals 310. One ofthe input terminals is grounded, and the other is connected to acoupling capacitor 312. The capacitor 312 has a capacity of 2microfarads, for example, and it is connected to the base electrode ofthe transistor 300. The transistors 300 and 302 in the latter embodimentare of the PNP type.

The emitter of the transistor 300 is grounded, and the collector isconnected to a resistor 313 and to a resistor 314. The resistor 313 may,for example, have a resistance I of 2.7 kilo-ohms, and it is connectedto the negative terminal of a 1.25 volt direct voltage source. Theresistor 314 may have a maximum resistance of 135 kilo-ohms, forexample, and it is connected back to the base of the transistor 300.

The collector of the transistor 300 is connected to a coupling capacitor316. The coupling capacitor may have a capacity, for example of 2microfarads, and it is connected to the base of the transistor 302. Theemitter of the transistor 302 is grounded, and the collector of thetransistor is connected to an output terminal 318. The collector of thetransistor 302 is also connected to a grounded capacitor 320 and to aresistor 322. The capacitor 320 may, for example, have a capacitance of107 microfarads. The resistor 322 may have a maximum resistance, forexample, of 210 kilo-ohms.

As shown in FIGURE 8, the circuit of FIGURE 7 is laid out appropriatelyon the substrate 304. Thin-film resistances and conductors are used toprovide an integrated circuit structure. Shorting tabs 330' are formedon the resistor 322 and on the resistor 314. As in the previousembodiments, these shorting tabs may be connected to the adjacentrespective conductors, so that the associated resistors may have adesired value to match the characteristics of the transistors 300 and302.

The invention provides, therefore, an improved miniaturized hearing aidinstrument which may be mounted directly in the ear of the user; andwhich is advantageous in that it may be constructed simply, practically,and economically, to provide a rugged, impervious unit. The unit of theinvention is susceptible to rough usage without damage, and it is alsohighly resistant to adverse effects of moisture and other corrosiveagents.

While particular embodiments of the invention have been shown anddescribed, modifications may be made, and the following claims areintended to cover all such modifications.

What is claimed is:

1. In a hearing aid unit which includes a microphone and a receivermeans, an amplifier section electronically coupling said microphone tosaid receiver means and including in combination: a panel-like substratemember formed of insulating material; at least one transistor mounted onsaid substrate member; a plurality of resistances mounted on saidsubstrate member as film-like deposits; a plurality of conductorsinterconnecting said transistor and said resistances and mounted on saidsubstrate member as film-like deposits; and a plurality of electrical-1yconductive tabs formed over at least one of said resistances at spacedpoints therealong and adjacent to at least one of said conductors, saidtabs being adapted to be selectively coupled to the adjacent conductorto adjust to the value of such resistance.

2. The structure of claim 1 in which said amplifier section isencapsulated in a material to protect said amplifier section.

3. The structure of claim 1 including a casing in which said amplifiersection is mounted, with said casing including a detachable earpiece forthe receiver means which is shaped to extend into the ear canal of thewearer to support the hearing aid within the ear.

References Cited by the Examiner UNITED STATES PATENTS 2,999,136 9/1961Holt et al 179107 3,070,762 12/1962 Evans 317101 3,178,804 .4/1965Ullery et al 317101 OTHER REFERENCES Conway: Electronic Engineering,Resistors for Deposited Circuit Techniques, November 1949.

KATHLEEN H. CLAFFY, Primary Examiner.

ROBERT H. ROSE, Examiner.

S. I. BOR, Assistant Examiner.

1. IN A HEARING AID UNIT WHICH INCLUDES A MICROPHONE AND A RECEIVERMEANS, AN AMPLIFIER SECTION ELECTRONICALLY COUPLING SAID MICROPHONE TOSAID RECEIVER MEANS AND INCLUDING IN COMBINATION: A PANEL-LIKE SUBSTRATEMEMBER FORMED OF INSULATING MATERIAL; AT LEAST ONE TRANSISTOR MOUNTED ONSAID SUBSTRATE MEMBER; A PLURALITY OF RESISTANCES MOUNTED ON SAIDSUBSTRATE MEMBER AS FILM-LIKE DEPOSITS; A PLURALITY OF CONDUCTORSINTERCONNECTING SAID TRANSISTOR AND SAID RESISTANCES AND MOUNTED ON SAIDSUBSTRATE MEMBER AS FILM-LIKE DEPOSITS; AND A PLURALITY OF ELECTRICALLYCONDUCTIVE TABS FORMED OVER AT LEAST ONE OF SAID RESISTANCES AT SPACEDPOINTS THEREALONG AND ADJACENT TO AT LEAST ONE OF SAID CONDUCTORS, SAIDTABS BEING ADAPTED TO BE SELECTIVELY COUPLED TO THE ADJACENT CONDUCTORTO ADJUST TO THE VALUE OF SUCH RESISTANCE.